1. Field of the Invention
This invention relates to an apparatus for detecting ophthalmic diseases in the lens of a patient's eye, and more particularly to an apparatus for detecting ophthalmic diseases by irradiating a laser beam via an optical system at one spot in the interior of a patient's eye, and detecting the laser light back-scattered therefrom.
2. Description of the Prior Art
Cataracts are a common ophthalmic disease in which protein particles normally found in human crystalline lenses increase in size causing turbidity in the lens. Measuring the size and diameter of these protein particles is essential to effecting early detection of a cataract condition and to preparing preventative medical treatment thereof.
A human eye comprises transparent elements such as a cornea, crystalline lens, etc. Fine protein particles float amongst these transparent elements and exhibit Brownian movement. In normal disease-free eyes the protein particles are distributed in the form of small diameter particles, however in turbid eyes the particles are of a larger diameter.
There is known in the art an apparatus for measuring the diameter of protein particles in the human eye which comprises a laser for generating and then imaging a laser beam on a selected portion of the crystalline lens of the eye of a patient to be measured. Protein particles exhibiting Brownian movement pass through the portion of the lens of the eye on which the laser beam is focussed causing the back-scattering thereof. Part of the laser light back-scattered in this manner is directed toward the eyepiece of a binocular microscope for monitoring, and another part thereof is directed toward a photomultiplier which converts the intensity of the back-scattered light into an electrical signal. This signal is input to an autocorrelator which determines an autocorrelation function with respect to the fluctuation of the intensity of the back-scattered beam over time. The thus obtained correlation value is then used to calculate the relaxation time of the fluctuation of the intensity of the back-scattered beam. Accordingly, a diffusion coefficient may be further derived based thereon which may then be used to determine the diameter of the protein particles.
According to a prior art ophthalmic disease detection apparatus of this type, it is possible to measure the average diameter of the protein particles, however the measuring of the distribution of the particles in the crystalline lens remains problematic.